1. Field of the Invention.
The present invention relates to apparatuses and methods for identifying personnel and, more particularly, to apparatuses and methods for identifying personnel based on visual characteristics of the irises of their eyes.
2. Description of the Related Art.
Iris recognition, or “iris capture” is a method of biometric personal identification that uses pattern recognition algorithms based on images of at least one of the irises of an individual's eyes. Iris recognition uses camera technology to produce images of the details of the iris. These images are converted into digital templates and provide mathematical representations of the iris that are used to identify individuals.
Many iris capture systems with low levels of intrusiveness have been proposed to extend the operational range for iris capture in recent years. For example, a system has been proposed that consists of multiple synchronized high-speed, high-resolution, and narrow-field-of-view (NFOV) video cameras, in which system focus is fixed at a portal about three meters away from the camera. This is the first system that could be used in practice for iris capture over long distances with a high throughput (e.g., twenty persons per minute). However, the depth of field (DOF) for each user is limited (e.g., five to twelve centimeters). With the limited DOF, it is possible that a same user would need to pass the portal multiple times before a clear iris image is captured.
Other types of systems employ one high resolution camera with either an autofocus or a fixed focus lens for the capture. The depth information of the subject is usually needed in these systems, which can be estimated implicitly based on the scale or the size of the captured two-dimensional face, or can be computed based on a pair of high speed video cameras using stereo vision. Because the acquired depth information based on these methods is not very accurate, these systems are not robust enough for practical use. For example, the feature matching in the stereo cameras is not always accurate under different lighting conditions. As a result, the robust sub-pixel matching is not easy to achieve in practice. Furthermore, the accuracy of a stereo vision system also depends on the length of the baseline. High accuracy would require a longer baseline, which make it impossible to build a compact iris capture system for many security applications.
Even though cameras with high shutter speed are often used in these systems, users still need to remain still for several seconds so that the high quality iris image can be captured. This is because defocus blur can easily happen when a moving subject is captured with a significant amount of system delay because of the slow movements of the pan-tilt unit or because of a long autofocus time. The accurate depth information (i.e., distance from the user to the camera) provided by these systems could be used for iris deblurring and therefore to enhance the performance of the whole system.
What is neither disclosed nor suggested in the art is an iris capture system with an extended operational range, and that does not rely on the person remaining motionless for a period of a few seconds or more.